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Mathlib.Algebra.Category.Ring.Limits

The category of (commutative) rings has all limits #

Further, these limits are preserved by the forgetful functor --- that is, the underlying types are just the limits in the category of types.

Some definitions may be extremely slow to elaborate, when the target type to be constructed is complicated and when the type of the term given in the definition is also complicated and does not obviously match the target type. In this case, instead of just giving the term, prefixing it with by apply may speed up things considerably as the types are not elaborated in the same order.

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    The flat sections of a functor into SemiRingCat form a subsemiring of all sections.

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      limit.π (F ⋙ forget SemiRingCat) j as a RingHom.

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        Construction of a limit cone in SemiRingCat. (Internal use only; use the limits API.)

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          Witness that the limit cone in SemiRingCat is a limit cone. (Internal use only; use the limits API.)

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            If J is u-small, SemiRingCat.{u} has limits of shape J.

            We show that the forgetful functor CommSemiRingCatSemiRingCat creates limits.

            All we need to do is notice that the limit point has a CommSemiring instance available, and then reuse the existing limit.

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            If J is u-small, CommSemiRingCat.{u} has limits of shape J.

            The forgetful functor from rings to types preserves all limits. (That is, the underlying types could have been computed instead as limits in the category of types.)

            The flat sections of a functor into RingCat form a subring of all sections.

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              We show that the forgetful functor CommRingCatRingCat creates limits.

              All we need to do is notice that the limit point has a Ring instance available, and then reuse the existing limit.

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              If J is u-small, RingCat.{u} has limits of shape J.

              The forgetful functor from rings to types preserves all limits. (That is, the underlying types could have been computed instead as limits in the category of types.)

              We show that the forgetful functor CommRingCatRingCat creates limits.

              All we need to do is notice that the limit point has a CommRing instance available, and then reuse the existing limit.

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              If J is u-small, CommRingCat.{u} has limits of shape J.

              The forgetful functor from commutative rings to rings preserves all limits. (That is, the underlying rings could have been computed instead as limits in the category of rings.)

              The forgetful functor from commutative rings to commutative semirings preserves all limits. (That is, the underlying commutative semirings could have been computed instead as limits in the category of commutative semirings.)

              The forgetful functor from commutative rings to types preserves all limits. (That is, the underlying types could have been computed instead as limits in the category of types.)